Helical barbed tape is used to create a substantially impenetrable barrier in locations where security is an important factor. The helical barbed tape is defined by an elongated helix or coil wherein the plane of the tape is aligned generally perpendicular to the axis of the helix. Flat barbs extend angularly outward from opposed sides of the tape and are angularly offset from the plane of the tape.
Helical barbed tape has become a widely accepted form of security at many military installations and prisons. One or more elongated coils of the barbed tape may be stretched across an open area to define a barrier. Alternatively, one or more coils of the barbed tape may be stretched adjacent to the base of a fence or wall to prevent a person from scaling the structure. In many situations a coil of the barbed tape may be mounted to the top of a fence or wall. This latter application has been used extensively in nonmilitary and non-institutional use. For example, many storage yards and warehouses are surrounded by chain link fences having a continuous strand of helical barbed tape mounted to the top. The helical barbed tape may be employed in single coils or in multiple coils. In one known form, a small coil may be concentrically mounted within a larger coil with the respective helices being generated in opposite directions.
A relevant example of a helical barbed tape is shown in U.S. Pat. No. 3,463,455 which issued to P. T. Meckel on Aug. 26, 1969. U.S. Pat. No. 3,463,455 indicates that the barbed tape unit may define a true helix of generally circular configuration, or alternatively may define a generally eliptical or polygonal coil. The disclosure of U.S. Pat. No. 3,463,455 does not define the manufacturing technique by which the generally helical configuration is achieved. However, it is believed that the art as developed at the time U.S. Pat. No. 3,463,455 issued employed an apparatus that repeatedly hammered into one side of the tape to gradually deform the tape into the generally helical configuration disclosed in U.S. Pat. No. 3,463,455. This prior art manufacturing technique created substantial stresses on both the manufacturing machine and on the barbed taped. As a result, damage to both the tape and to the machine was likely. This process also was quite slow and required substantial quality control testing to ensure that a substantially uniform coil was being developed.
An apparatus and method for forming barbed tape is shown in U.S. Pat. No. 4,028,925 which issued to Michael R. Mainiero on June 14, 1977. The method disclosed in U.S. Pat. No. 4,028,925 involved mechanically clamping adjacent sections of a flat straight metallic strip and edge bending the adjacent sections relative to one another a controlled angular amount such that the adjacent sections remain substantially in their initial flat plane. The method and apparatus disclosed in U.S. Pat. No. 4,028,925 only is capable of forming a generally polygonal coil, and is not capable of forming a true helix with circular coils.
The barbed tape that is acceptable for military applications is defined in United Stated Specification Mil-B-52775. This specification defines the acceptable materials and dimensions and depicts both the circular and polygonal configurations of the helix. Mil-B-52775 does not define a method of manufacture. This specification has effectively become the standard for many nonmilitary applications of barbed tape.
Virtually all applications of helical barbed tape, including those manufactured to the standards of Mil-B-52775, employ a stainless steel tape formed into a polygonal coiled configuration. This configuration has been generally universally accepted because of the relative ease of forming the polygonal structure and the relative difficulty of reliably forming a uniform circular helical structure.
Despite its wide acceptance, the polygonal barbed tape has several disadvantages. The most severe disadvantage concerns the structural effects of placing the bends in the tape to define the corners of the polygon. More particularly, the bends of necessity form crimps or ripples adjacent the radially inside edge of the tape. Conversely, the radially outermost edge of the tape is stretched through the bend at a point directly opposite the crimp or ripple. The inherent brittleness of the hard stainless steel tape creates a substantial probability of cracking along the radially outermost edge of the tape at the point of the bend. These cracks will be aligned in a generally radial direction. In view of this tendency to crack, the barbed tape must be subjected to extensive quality control which adds to the manufacturing costs. In many instances, these cracks will be very small and will not be readily visible to the unaided human eye. In fact, some cracks will not extend entirely through the metal but will merely be formed in one or both opposed surfaces of the tape adjacent the outer edge of the bend. Although these small cracks may be initially inconsequential, they can have severe implications after the tape has been put into use. More particularly, the barbed tape will inevitably vibrate in response to wind and other ambient conditions. These vibrations will cause the microscopic cracks to propagate. After a relatively short period of time, the initially microscopic crack can extend completely across the tape. These breaks in the tape effectively prevent the tape from fulfilling its security function.
In addition to the potential for cracks, the bends may also sever the protective coatings put on certain metallic materials. By severing this protective layer, a more vulnerable interior layer of metallic material may be exposed to the actions of the environment.
Another deficiency of the polygonal barbed tape coils is that the polygonal structure inherently must be formed as part of an intermittent action. The repeated stopping and starting of the machine and the tape passing therethrough is slow and creates substantial wear on the various parts being alternately accelerated and decelerated.
Certain barbed tapes have been developed into a circular configuration by forming the central part of the barbed tape around a core wire. The core wire will thus support the tape and the tape will move with the wire. The wire can thus be formed into a circular helical coil with the tape conforming to the circular helical configuration of the wire. This structure is shown, for example, in U.S. Pat. No. 2,908,484 which issued to Uhl on Oct. 13, 1959. The combination of the barbed tape with the core wire also has several significant disadvantages. For example, the presence of the core wire adds significantly to the weight and cost of the structure. Furthermore, the presence of the core wire prevents the compact collapsing which is possible with the flat barbed tape. Thus, this type of barbed tape requires substantially more storage area, which can be of critical importance in many military applications where a large amount of tape must be transported under demanding conditions to a distant location for prompt deployment. Another disadvantage results from the additional structural support caused by the core wire. More particularly, the stronger barbed tape product having a core wire disposed therein will not be as likely to collapse upon an intruder attempting to pass therethrough.
In view of the above, it is an object of the subject invention to provide a process for producing a substantially circular flat barbed tape.
It is an additional object of the subject invention to provide an apparatus for producing a substantially circular flat barbed tape.
Another object of the subject invention is to provide an apparatus for continuously producing a helical barbed tape.
Still another object of the subject invention is to provide a flat helical barbed tape of substantially uniform cross section along its length.
An additional object of the subject invention is to provide a helical barbed tape substantially free of cracks adjacent the radially outer edge thereof.